Method of cutting bevel gears



Jan. 1, 1929. Y 1,696,930

E. WILDHABER .KTHOD OF CUTTING BEV-EL GEARS ,4 mvENToR l r Efwstwdfzam @L45 F246 "L Al l) Patented Jan. 1, 1929.

UNITED Asfrarss ERNEST WILDHABER, F BROOKLYN, NEW YORK, ASSIGNOR TO GLEASON WORKS, 0F

Parent oFricE.

ROCHESTER, 'NEW YORK, A CORFORATION OF NEVI YORK.

METHOD OF CUTTING BEVEL GEARS.

Application filed March 1, 1927. Serial No. 171,774.

The present invention relates to a method ot' generating bevel gears and particularly to a method of generating straight tooth bevel gears.

The primary object of this invention is to eii'ect a saving in time in the generation ot bevel gears. Heretoiore, bevel gears have been generated in an operation in which the pitch surface ot' the blank rolls on the-pitch surface of a basic gear represented by the tools. I have found tl at the amount ot nievement required to fully generate the tootl profiles of a bevel gear may be materially reduced by rolling the gear as with a surface other than its pitch surface on the pitch surface of the basic gear represented by the tools. Reducing the amount ot roll required to fully generate the tooth proiiles means, of course, a considerable saving in production time.

In the present invention the blank is rolled as with a cone surface of smaller dimension that its pitch cone surface on the pitch surface of the basicv gear' represented by the tools and, preferably, the rolling cone surface ot' the blank is so selected that in the center of the roll the tools Contact with the proliles of the tooth surfaces being generated in points midway the height of said profiles.

The accompanying drawings show spec/iiically the application ot' the present invention to the production ot straight tooth bevel gears with reciprocating planing tools. it will be understood, however, that this invention is capable ot use in the production ot curved -tooth bevel gears and with other forms of tools.

In the drawings Figure l is a diagrammatic view illustrating the present method ot generating a straight toetlrbevel gear with a pair ot reciprocating planing tools;

F igure 2 is a similar view showing by way olf comparison the method of generating a straight tooth bevel gear with pair ot planing tools Vaccording to the principles oi this invention Figures l and 4 are a diagrammatic end elevation and side view, respectively, illustrating further the relationship between the blank and basic gear in the generation of bevel gears according to this invention; and A Gand 7 are' diagramifi'iatic lviei'vs ',yne varimj'is relative positions el: the

planing tools and blankin the generation of opposite side tooth surfaces of involute profile on al bevel gea-r blank. l

in the teneration oi bevel gears, a cutting motion is imparted to the tool or tools and simultaneously the tool or tools and the blank are moved.relatively to each other as though the blank were rolling with a basic gear `represented by the t-ool or tools. ln this rolling motion, the cutting edge comes into cutting contact with the tooth surface in a point at the top or bottom of the tooth profile and during the generating roll the point of contact moves along the proiile until the tooth surface been'tully generated.. This is illustrated diagrammatically in Figures to 7 in which the tools are shown as a pairot planing tools 1() and 1l, having iinish outting edges l2 and 13, respectively. yDuring the generating operation, the tools are reciprocated across the tace ot the blank, kindicated at 11i, in straight converging paths and simultaneously the tools and blank are moved relatively to each other as though the blank were rolling on a basic gear 15 represor-)tedv by the tools. The basic gear is usually a. crown gear or a nominal. crown gear, that is, a gear having a plane top surface and a conical pitch surface.

Figures 5, 6 and 7 show three positions of the tools and blank during the generation of a tooth 16 oi' the blank. Figure 5 shows a position in the beginning of the roll, where vthe tool 11 has ust started to cut the tooth surface 17 and where kthe tool 10 has not yet come into engagement with the opposite side tooth surface 18. Figure 6 shows the positions ot the tools and blank in the center oi the roll and Figure 7 shows the position .ot tools and blank when the tooth surfaces 17 andV 18 have beentully generated and the tool and bilankqare about to loe withdrawn relatively to each other to permit indexing oit the blank and return ofthe tools to their initial position tor generation ot' another tooth oit the blank.

Figure l illustratesthe present method ot g" yierat-ing bevel gears on a two tool genera-' tor. 20 designates a tooth of the blank and' 21 and 2Q the reciprocating.planing tools whose ti'nish cutting. edges rare designated as 23 and 24, respectively. The tooth 2O shown :isnt the pro" `ertions of a a bevel gear be producer. upon a tooth bevel gear generator'. ln this machine, the basic gear7 represented by the tools, and upon which the blank rolls during generation is a nominal crown gear, that is, a gear having a plane top surface and a conical pitch surface.

According to the present practise the gear is rolled with its pitch surface 2:5 on the pitch surface oi abasic crown gear represented by the tool. The pitch surface oft the nominal crown gear is so nearly a. plane that it may be represented by the straight line 26 in Figure 1. ln the center ot the roll the cutting edges 23 and 24 ot' the tools 21 and 22 contact with the profiles 27 and 28 ot the gear tooth in the points 29 and 30 which lie on the normal lines 31 and 32 passing through the point- P which is the instantaneous center of generation. In the present case, the generation of gears with teeth ot inyolute profile7 the lines 31 and 32 are also the lines ot action between the cutting tools and blank.

It will be noted that the points of contact 29 and 30 are located near the point or tip ot the tooth 20. In order to completely generate the side tooth surfaces of the tooth the tools 21 and 22 must travel from the dotted line positions indicated at 21 and 22 where the cutting edge of the tool 22 makes contact with the bottom of the tooth profile 28 to the dotted line positions 21 and 22" where the cutting edge ot the tool 21 makes contact with the bottom oit the tooth profile 2T. This total travel or total cradle roll is'equal to the distance G, in Figure 1.

I hare found that the amount ot roll required to tully generate the tooth surfaces can be very considerably reduced by rolling the blank not on its pitch cone but on another concentric cone which is so selected that in the -center of the roll the tools will contact with the tooth profile ot the blank in points aud 36 which are about in the center ot such profile. Here, thc rolling cone surface of the blankis the surface 8i' which is ot smaller dimension than the pitch surface 25. rlhe cone surface 37 rolls on the pitch surface of the basic gear represented by the tools. When the gears are generated in this way, the amount ot rolll required will be considerably reduced, as is evident from Figure 2. Here, 21:l and 2.2l indicates the extreme lett hand positions of the tools 21 and 22 where the tool 22 is making the nishing cut upon the bottom ot the tooth prolile 2S and 212 and 222 indicate the extreme right hand position ot the tools where the tool 21 makes the finishing cut on the bottom ot' the prolile 27.

The amount ot' roll required with the present invention is reduced trom Gr ot Figure 1 to G of Figure 2. P is the new instantaneous center of generation. In the present case where the tooth profiles generated are in volutes, the points and SG., where the tools neeaeeo Contact with the tooth profiles at the center of the roll7 will lie approximately midway of the lines ot action 31 and 32. ln many cases, with the present invention the amount of rollcan be reduced as much as 30% over the amount of roll required with the present practise, which means a. very considerable sav- .ing` in the cutting time. y

The dimensions ot the cone upon which each member of a pair ot bevel gears mustbe rolled to attain the purposes of this invention and the other dimensions ot thes-e gears can be determined as follows: Reference is made particularly to Figures 3 and 4. 40 indicates a portion oit the blank to be cut, of which one tooth is shown at 41. 42 is the apex ot the blank and 43 its axis. 44 designates the axis of the basic gear with which the blank is to be rolled during generation. R indicates the root angle of the blank and l? its pitch cone angle when rolling with a mate gear. ln the drawings, the blank is shown as so positioned that its axis makes an angle with a plane passing through the line Y perpendicular to the axis 44 of the basic gear, equal to its root angle. In other words, the blank is generated conjugate to a nominal crown gear by tools, the top or points of which travel in a plane passing through the line 45 perpendicular to the axis 44 et the crown gear.

l) is, as stated, the pitch cone angle ot the blank when rolling with a mate gear. The angle lit-+L is the angle of the cone upon which the blank is rolled during generation. Angle L is itselt 'the complement ot the cone angle (90o-L) of the nominal crown gear upon which the blank is rolled during generation. y

Let a equal the pressure angle et the tools used in generating the gear. inasmuch as the gear rolls with a conc other than its pitch cone, the pressure angle ot' the gear `when generating with the point P as the instan- Y taneous center will be diilerent from the pres sure angle u/ of the tool. Let c equal the pressure angle when generating the pitch lines. 90o minus e is the angle included between thc plane 46-42-47 and the plane ot pressure, that is, the plane normal to the tooth siu'itacc being cut and including` the apex 42 ot the blank. ln `Figure 3, 423 is the projection et the axis ot the blank to said plane of pressure. Angle 46-4249 is what might be called the base cone angle (7)) in involute gears.' lVhether. the gears are truly involute or not7 the same relation will exist between the base cone angles ot mate gears as between their pitch angles, namely the proportion ot the sines oi the base conc angles (-5.111 I) p t \s1n t] equals the ratio of the respective tooth nurnbersof the mate gear Where n and N y are the tooth numbers ot pinion and gear re spectively and b and. I), a base cone angle of tooth of the mate gear when generated in the manner described herein.

Angle e differs slightly from the pressure.

angle a of the tools. It depends to a certain extent on the angle p which is the angle 1ncluded in the plane passing through line 45 tan e= tan a cos Iii-sin e sin L tan r1,

perpendicular to the crown gear axis 44,. by the edge of the crown gear tooth with a line drawn centrally through the gear tooth belng. generated, that is, the line 50 of `Figure 3.

- In other'words, the angle e isa measure of the phase of the generating' roll.-

The angle can be determined approximately with sufficient accuracy by assuming that the actual pressure angle is equal to a. The angle f then equals:

d-Li` l Y dIsinacosalpLtana (3)' and: d L 2 cos e (bzsinacosaf 4) Angle e can then be determined as follows:

COS qb In figuring a job', the instantaneous center or rolling center P of the gear to be cut is so assumed that in the center of the roll the points of Contact 35* and 36 between the tools and the tooth surfaces to be cut will lie midway the heightof the tooth profiles, as shown in Figure 2. The angle L can be determined as follows:

tion l, above, and the angle e can be deter-y mined from equation The angle L1, referring to the mate gear, is then first approximately determined from the equation 2, e, being. Iassumed equal to a. Angle L1 so determined is then .used in equation 4L to determine the angle (t, for the mate gear, and with this angle, the angle e,` can be determined from .equation 5. The angle el resulting from equation 5 is then used in equation 2 for more accurately determining angle LL. In the way described, the cone angles of the cones lupon which each member of the pair of mate gears is to be rolled during generation, can be determined.

lVhen gears are cut according to this invention with tools of standard pressure angles, the pressure angles of the gears will be found to be slightly larger than of the tools. The increase in pressure angle on the gears cos qS cos L-ttan sin L. (5)V over t-he tool pressure angles diminishes, however, with increasing numbers of teeth in the gears and with increasing ratios, as is desirable. By using tools of special pressure angles, a further saving in time can be effectedv over that in wliichtools of standard pressure angle are employed.

While the present invention has beende.- l

scribed particularly with reference to the generation of straight tooth bevel gears it will be evident that it can be applied also to the production of curved tooth bevel gears, either by the use of planing tools which move in. curved paths across the face of the blank during the cut, or by the use of tools of the rotary annular face mill type,- where the cutting blades are annular'ly arranged and the tool rotates on its during the cutting operation. The principles of this invention are applicable, moreover, not only tothe production of bevel gears with planing and milling tools but also with grinding tools and the tools need not be of straight profile but may have any desired curvature.

In general, while I have described my invention with reference to a particular embodiment, it will be understood that it is not intended to limit the invention to the embodiment described, but rthat this application is intended to -cover any variations, uses, or adaptations of my invention, following, in general, the principles of the invention and including such departures from.y the present disclosure as come wit-hin known or customary practise in the gear art and may be applied to the essential features hereinbefore set forth and as fall within the scope of the invention and the limits of the appended claims.

Having I claim is: y

1. The method of producing a bevel gear which consists in cuttingits side tooth sun thus described my invention, what izo faces two sides simultaneously by moving a pair of cutting edges across the face of a tapered gear blank while imparting a relative rolling motion between the cutting edges and blank in which the blank rolls with a cone surface of smaller dimension than its pitch cone surface on the pitch surface of a basic gear represented bysaid cutting edges, thereby to reduce the amount of roll required to generate the tooth profiles.

2. The method of producing` a bevel gear which consists in cutting its side tooth surfaces two sides simultaneously by moving a pair of cutting edges across the face of a tapered gear blank while iniparting a rela-- tive rolling motion between the cutting edges and blank in which the blank rolls with a cone surface of smaller dimension than its pitch cone surface on the pitch surface of a basic gear, represented by the cutting edges, having a plane top surface and a conical pitch surface, thereby to reduce the amountof roll required to generate the tooth profiles.

8. Illhe method of producingl a bevel gear which consists in reciprocating a pair of cutting'edges adapted to finish cut opposite side tooth faces of the blank, in straight converging paths across the face of a tapered gear blank while imparting a relative rolling motion between the cutting edges and blank in which the blank rolls with a cone surface of maller dimension than its pitch cone surface on the pitch surface of abasic gear represented by said cutting edges, thereby to reduce the amount of roll required to generate the tooth profiles.

t. The method of producing a bevel gear which consists in reciprocating a pair of cutting edges adapted to finish cut opposite side tooth faces of the blank, in straight converging paths across the face of a tapered gear blank while imparting a relative rolling inot-ion between the cutting edges and blank in which the blank rolls with a cone surface of smaller dimension than it-s pitch cone surface on the pitch surface of a basic gear, represented by the cutting edges, having a plane top surface and a conical pitch surface, thereby to reduce the amount of roll required to generate the tooth profiles.

5. The method of producing a bevel gear which consists in cutting its side tooth surfaces two sides siniultaneously by moving a pair of cutting edges across the face of a tapered gear blank while imparting a relative rolling motion between the cutting ed ges and blank in which the blank rolls with a cone other than its pitch cone on the pit-ch surface, of a basic gear represented by the cutting jedges, said rolling cone surface of the blank being so selected that in the center of the roll, the cutting edges contact with opposite side tooth profiles of the blank in points appioximately vmidway the height of said prolifesd 6. The method of producing a. bevel gear which consists in cutting its side tooth surfaces two sides simultaneously by movingl a pair of cutting edges across the face of a tapered gear blank while imparting a relative rolling movement between the cutting edges and blank, in which the blank rolls with a cone other than its pitch cone on the pitch surface of a basic gear, represented by the .cutting edges, having a plane top surface and a. conical pitch surface, said rolling cone surface of the blank being so Vselected that in the center of the roll, the cutting edges contact with opposite side tooth profiles of the blank in points approximately midway the height of said profiles.

7. The method of producing a bevel gear which consists in reciprocating a pair of planing tools adapted to finish cut opposite side tooth faces of a blank, in straight con verging paths across the face of a tapered gear blank while imparting a relative rolling motion between the tools and blank in which the blank rolls with a cone other than its pitch cone on the pitch surface of a basic gear represented by the tools, said rolling cone surface of the blank being so selected that in the center of the roll, the tools contact with oppo site side tooth profiles of the blank in points approximately midway the height of said profiles.

S. The method of producing a bevel gear which consists in reciprocating a pair of planing tools, adapted to finish cut opposite side vtooth faces of the blank, in straight converg ing paths across the face of a tapered gear blank while imparting a relative rolling movement between the tools and blank in which the blank rolls with a cone other than its pitch cone on the pitch surface of a basic gear, represented by the tools, having a plane top surface and a conical pitch surface, the rolling cone surface of the blank being so sen lected that in the center of the roll the tools contactvwith opposite side tooth profiles of the blank in points approximately midway the height of said profiles.

9. The method of generating a bevel gear which consists in positioning a pair of cutting edges and a tapered gear blank relatively to each other so that in the center of the roll the points of contact between the cutting edges and the tooth profiles being generated lie approximately midway of the lines Vof action, and in imparting a cutting motion to the cutting edges while rolling the blank as with a cone other than its pitch cone on the pitch surface of the basic gear represented by the tools.

l0. The method of generating a bevel gear with teeth of involute profile which consists in *positioning a pair of cutting edges and a. ta-

pered gear blank relatively to each other so that in the center of the roll the points of tact between the cutting edges and the tooth profiles being generated lie approximately midway of the lines of action and imparting a cutting movement to the cutting edges while simultaneously producing a relative rolling motion between the tools and blank in which the blank rolls as with a cone other than its pitch cone on the pitch surface of a basic gear,

represented by the tools, having a plane top surface and a conical pitch surface.

l1. The method of generating a bevel gear with teeth of involute proiile which consists in positioning a pair of planing tools and a tapered gear blank relatively to each other so that in the center of the roll the points of con tact between the cutting edges of the tools and the tooth profiles being generated lie approximately midway of the lines of action, and in reciprocating the tools in straight con-` verging paths across the face of the blank While producing a relative rolling motion between the tools and blank in which the blank rolls with a cone other than its pitch cone on the pitch surface of a basic gear, represented by the tools, having a plane top surface and a conical pitch surface.

l2. The method of generating a bevel gear with teeth of involute profile which consists in positioning a pair of planing tools and a tapered gear blank relatively to each other so that in the center ofthe roll the points of contact between the cutting edges of the tools and the tooth proliles being generated lie approximately midway of the lines of action, and in reciprocating the tools in straight converging paths across the face of the blank while producing a relative rolling motion between the tools and blank in which the blank rolls with a cone other than its pitch cone on the pitch surface of a basic gear, represented by the tools.

13. The method of generating a bevel gear with teeth ot involute proiile which consists in positioning a pair of planing tools and a tapered gear blank relatively to each other .so that in the center of the roll the points of contact between the cutting edges of the tools and the tooth profiles being generated lie approximately midway ot the lines of action, and in reciprocating the tools across the face of the blank while producing a relative rolling 1notion between the tools and blank in which the blank rolls with a cone other than its pitch.

ERNEST WILDHABER. 

